1. Field of the Invention
The present invention relates generally to a pulse width modulating circuit, and is directed more particularly to a pulse width modulating circuit suitable for use in remote control applications such as, for example, the sound volume of a television receiver.
2. Description of the Prior Art
In the prior art when, for example, the sound volume of a television receiver is remotely controlled, each time a viewer of the television receiver remotely controls the sound volume, a transmitter of a remote control device transmits an ultrasonic or a supersonic pulse P.sub.a as shown in FIG. 1A. The supersonic pulse P.sub.a is received by the television receiver which then produces a modulating pulse P.sub.b shown in FIG. 1B each time it receives a supersonic pulse P.sub.a. The modulating pulse P.sub.b is fed to a pulse width modulating (PWM) circuit which then produces a pulse width modulated (PWM) pulse P.sub.c whose pulse width is changed for example, is increased at each arrival of the supersonic pulse P.sub.a as shown in FIG. 1C. The pulse width modulated pulse P.sub.c is then integrated to provide a DC voltage E.sub.d whose level increases at every supersonic pulse P.sub.a as shown in FIG. 1D. This DC voltage E.sub.d may be used to control the gain of an audio amplifier.
Thus, the sound volume of the television receiver can be increased each time a supersonic pulse P.sub.a is generated. The sound volume can be similarly decreased using another supersonic pulse not shown.
In order to achieve such pulse width modulation control the prior art combines an up-counter, up-down counter, exclusive OR circuit and other circuits. This combination is, however, expensive.